1. Field of the Invention
The present invention relates to a light-emitting apparatus comprising a light-emitting device that emits fluorescence or phosphoresce upon application of an electric field thereto and includes a pair of electrodes and a film containing an organic compound (hereinafter, an organic compound layer) that is sandwiched between the pair of electrodes, and to a method of fabricating the light-emitting apparatus. In this specification, the term “light-emitting apparatus” includes an image display apparatus, a light-emitting device, or a light source (including a lighting system). Also, the following modules are included in the light-emitting apparatus: a module obtained by attaching a connector such as an FPC (flexible printed circuit), a TAB (tape automated bonding) tape, or a TCP (tape carrier package) to a light-emitting device; a module obtained by providing a PWB (printed wiring board) with a tip of a TAB tape or a TCP; and a module obtained by mounting directly an IC (integrated circuit) to a light-emitting device by the COG (chip on glass) system.
2. Description of the Related Art
A light-emitting device using an organic compound as a luminous body, which is characterized by its thinness and light-weight, fast response, direct current low voltage driving, and so on is expected to be applied to next-generation flat panel displays. Particularly, a light-emitting apparatus in which light-emitting devices are arranged in a matrix configuration is considered to be superior to the conventional liquid crystal display devices for its wide viewable angle and excellent visibility.
The luminescent mechanism of a light-emitting device is as follows: an electric field is applied to a pair of electrodes that sandwich an organic compound layer, and electrons injected from a cathode and holes injected from an anode are re-combined at the luminescent center of the organic compound layer to form molecular excitons, and then the molecular excitons revert to a ground state while radiating energy, consequently, luminescence radiation takes place in the organic compound layer. Known excitation states are an excited singlet state and an excited triplet state whose electronic level is made up of many vibrational and rotational levels. The luminescence radiation is allowed to take place by reverting from either state to the ground state.
A light-emitting device constructed of a plurality of light-emitting devices being arranged in a matrix configuration may be operated by one of well-known driving systems such as a passive matrix drive and an active matrix drive. However, when a pixel density increases, it may be preferable to use an active matrix type system in which a switch is provided in every pixel (or every dot) because it can be driven at a low voltage.
In case of forming an active matrix type light-emitting apparatus, a thin film transistor (TFT) is formed over a substrate having an insulating surface as a switching element and an EL device that comprises a pixel electrode connected electrically to the TFT as an anode and a cathode is formed in a matrix configuration.
In a manufacturing factory where a TFT is formed over a substrate having an insulating surface and a manufacturing factory where an integrated circuit is formed over a semiconductor substrate, a manufacturer pays an attention to keep the factory in high cleanliness and to prevent impurities from being mixed into a delicate device. Particularly, they pay an attention to prevent an alkali metal element that gives a semiconductor device an adverse effect.
On the other hand, for forming an EL device, it is preferable that a small function material is used as a cathode, especially, an alkali metal element is proper, and it is necessary to form an organic compound layer as a light-emitting layer.
Therefore in case of fabricating a TFT and an EL element over a substrate, a possible solution to the problem of contamination is to separate a installation site of an equipment for fabricating a TFT from an installation site of an equipment for fabricating an EL device. For example, using different purifiers by providing partition between devices, separating buildings in which the equipment are installed, or separating a factory itself can be considered.
In case of separating equipment, a problem will arise that substrates should be transported between the installation sites, and there is a risk of electrostatic discharge damage and adhesion of dust on a substrate during transportation of the substrates.
Further, since a substrate, an organic insulating film, and an inorganic insulating film are insulators, static electricity easily charges their surfaces. Due to this, there is a threat of adhesion of dust on the charged-surface or generating electrostatic discharge if the substrate, the organic insulating film, and the inorganic insulating film come into contact with another object.
Since an organic compound layer serving as a light-emitting layer has a thin film thickness, poor coverage easily occurs due to large irregularities of the surface, that is, large difference in level is produced.